1. Technical Field
The present invention relates to tympanoplasty, or the surgical reconstruction of the middle ear which restores or replaces the sound conducting mechanism. More particularly, the present invention relates to an improved method for preparing an ossicular replacement prosthesis, an improved ossicular replacement prosthetic device and a punch mechanism for removing tragal cartilage and applying the removed cartilage to the prosthetic device before the device is implanted in a patients ear.
2. Discussion of the Prior Art
Under normal circumstances, sound waves which strike the tympanic membrane (i.e. the ear drum) are transmitted through the ossicular chain of the middle ear (i.e. the malleus, the incus and the stapes) to a membrane which is stretched across the oval window of the inner ear. In this regard, reference should be made FIG. 1 of the accompanying drawings wherein a drawing of the inner ear is provided to facilitate an understanding of the structure involved. Behind the oval window membrane is fluid which fills the cochlea of the inner ear where the transmitted vibrations are translated into neural impulses. Sound transmission through the ossicular chain can become interrupted or non-functional due to a variety of diseases or injuries to the middle ear. Surgical reconstruction of the middle ear to restore or replace the sound conductive mechanism therethrough is called tympanoplasty. In cases where portions of the ossicles have become erroded, lost or otherwise non-functional, a plastic prosthetic device may be placed between the tympanic membrane and the head or footplate of a mobile stapes. An example of such prosthetic device may be found in U.S. Pat. No. 3,909,852 (Homsy). If the footplate is not mobile, the prosthetic device may be implanted between the drum and a graft placed over a drilled-out or fenestrated footplate. In either case, the ultimate goal is the restoration of the sound conduction function from the tympanic membrane to the oval window by means of a prosthetic device which replaces some or all of the ossicles. In FIG. 4a there is illustrated a typical prior art prosthetic device 10 implanted between the tympanic membrane and the head of the stapes. In FIG. 4b a typical prior art prosthetic device 11 is shown implanted between the tympanic membrane and the footplate of the stapes.
Ossicular replacement prosthetic devices take a variety of forms and are selected for implantation in accordance with the nature of the pathology and anotomical peculiarities of the patient. The present invention relates to only two types of such prosthetic devices, namely: the total ossicular replacement prosthesis (TORP) and the partial ossicular replacement prosthesis (PORP). The TORP, as its name implies, replaces the entire ossicular chain and fits between the tympanic membrane and the footplate (or fenestrated footplate) of the stapes, such as the prosthetic device 11 of FIG. 4b. This prosthetic device 11 is illustrated in greater detail in FIG. 2b and is shown to include a cylindrical shaft portion 14 terminating at one end in a circular flange 15 which faces the typanic membrane when the prosthesis is implanted. The opposite end of shaft 13 rests against the foot plate of the stapes when implanted. The PORP fits between the tympanic membrane and the head of a functioning stapes as illustrated by prosthetic device 10 illustrated in FIG. 4a. Prosthetic device 10 is illustrated in greater detail in FIG. 2a and includes a shaft 17 which terminates at its tympanic membrane-facing end in a flange 19 similar in configuration to flange 15 of prosthetic device 11. The opposite end of shaft 17 is provided with a generally cylindrical part extending longitudinally of the shaft so as to be able to receive the head of the functioning stapes. Each of prosthetic devices 10 and 11 take a variety of more specific configurations such as illustrated in FIGS. 3a through 3h, depending upon the particular anotomical features of the patient. The devices illustrated in FIGS. 3a, 3b, 3c and 3d represent PORP devices; the prosthetic devices illustrated in FIGS. 3e, 3f, 3g and 3h represent TORP devices. All of these prosthetic devices are typically constructed from a plastic material, or combination of plastic materials, that can be readily tolerated by the human body. Some of these plastics are porous and purposely designed to promote tissue ingrowth in order to stabilize the implant, much in the manner described in the aforementioned Homsy Patent. In all instances, however, the material employed must be capable of conducting sound from the tympanic membrane to the head or foot plate of the stapes.
A major problem associated with the utilization of the prosthetic devices illustrated in FIGS. 3a through 3h is the tendency toward rejection and subsequent extrusion (or perforation) of the implant when the plastic surface of the prosthesis comes into contact with the tympanic membrane or a graft which replaces this membrane. It has been found, in the prior art, that this problem can be alleviated by placing a thin slice of cartilage between the prosthesis and the tympanic membrane. This is illustrated in FIG. 5a for the PORP device and in FIG. 5b for the TORP device. In order to obtain this cartilage a surgeon must first make an incision in the leading edge of the tragus to expose the cartilage and its outer covering, the perchondrium. A piece of tragus is then removed with a scalpel making sure that the perchondrium is left intact. The cartilage is then trimmed and sewn onto the prosthesis as illustrated in FIG. 6a.
The cartilage is sewn onto the prosthesis in a manner which will bring the perichondrium of the finished implant in touch with the tympanic membrane. The cartilage is then trimmed to fit the dimensions of the flange.
This trimming procedure is illustrated in FIG. 6b and the final prosthesis, with the properly trimmed slice of cartilage, is illustrated in FIG. 6c.
There are numerous problems associated with the technique described above for obtaining the tragal cartilage and attaching it to the prosthesis. Since the procedure is performed by hand, it is a relatively time-consuming process which requires considerable dexterity on the part of the surgeon. In addition, although this technique is preferable to methods which do not use cartilage, the end product still interposes suture material between cartilage and the tympanic membrane or ear drum which could lead to rejection and extrusion. Further, since is is trimmed with a scalpel, the resulting cartilage plug has sharp edges which may lead to perforation of the ear drum. Finally, the suture employed for this procedure does not dissolve and consequently is always in contact with the drum, thereby promoting infection and utilmate extrusion.